I literally just had this discussion with the head of manufacturing here. In THEIR world, they know how long it takes to build widget X down to the second. They go all cross-eyed when I try to explain to them that 4 months of design time may be nowhere near as long as what is needed to design new widget Y, even if it's based on widget X. "But, why don't you know???" she cries.
Because, Karen, a lot can go wrong in 4 months when you are doing something you've never done before and have no idea if the concept is even going to work! You are asking me to have a magic crystal ball and I'm going to tell you, the ball is cracked, broken, filled with smoke... and, as it turns out, is a BOWLING BALL... so I can't do what you want. We can UPDATE you with our progress as time goes on and we learn more, but right now, our sight as to what we can do and commit to is about 1-2 weeks out... not 4 months.
Karen is not getting a Christmas card this year.
Don't be like Karen.
Don‘t be like Karen.
Let‘s make that a running gag for everyone whining about lead times ...